Single neurons in the medial superior temporal area (MST) of Rhesus monkeys have been found to show selective responses to visual stimuli simulating the motion seen as a result of observer self movement. In the monkey neurophysiology laboratory we are continuing studies of the responses of these neurons to visual stimuli. A number of computational models have been developed to account for the visuosensory response properties of MST neurons during the presentation of optic flow field stimuli. We have now collected data which samples the stimulus space at a higher resolution to determine whether MST neurons are sensitive to subtle changes which might indicate a shift in the heading of self movement. These data are being compared to the output of current models about MST response mechanisms (implemented at Bochum) to test those models on data sets which were not previously available. Our goal is to use the results of these comparisons to guide future neurophysiologic experiments, initially using purely visual stimuli, and later integrating non-visual heading cues introduced on the two-dimensional sled.